A human tooth comprises a crown and roots. The crown is the part of the tooth visible above the gumline while the roots are under the gums. The roots anchor the teeth to either the maxillary or mandibular bones. Within the roots are root canals which contain pulp. Pulp is live tissue which includes nerves and blood vessels.
The pulp may become infected and inflamed as a result of dental caries or physical trauma to the tooth. Endodontics is a branch of dentistry which treats teeth with diseased pulps. Endodontics is commonly referred to as root canal therapy. The goal of root canal therapy is to save the tooth by removing the diseased pulp. The root canal is then cleaned and filled. A crown or cap is typically placed on the tooth to protect the tooth and preserve its functionality.
In the prior art, porcelain fused metal ("PFM") systems are commonly used. In a conventional PFM system, a post and core are fashioned from one of a variety of suitable precious and non-precious metals. The post is made to snugly fit the root canal void and serves to anchor the core and crown. The core is built up onto the post and forms the support for the crown which replaces the injured tooth. The crown may be fashioned from porcelain (ceramic) material.
PFM systems enjoy excellent strength due to the metal post and excellent wear resistance due to the porcelain. However, a major drawback to PFM systems is the aesthetic appearance of the completed restoration. The enamel and dentin of a normal human tooth are slightly translucent which determines the natural look of a tooth. The metal post and core used in a PFM system reflects light passing through the artificial crown which results in the restoration looking unnatural.
A solution to this drawback of PFM systems is to replace the metal post with a ceramic material which simulates the translucency of normal teeth. An example is the CosmoPost.TM. system available from Ivoclar Vivadent, Ivoclar North America Inc. The post in this system is a zirconium oxide based ceramic, resulting in an aesthetically pleasing restoration. However, this system suffers from certain drawbacks. The posts are only available in preformed posts of a certain size and diameter. As a result, the dentist must perform the root canal therapy such that the root canal is the exact fit of the pre-formed post and to do so requires the use of proprietary root canal reamers.
Another solution to the aesthetic drawback of PFM systems is to use a carbon fibre based material such as the Composipost.TM. system available from Biodent of Quebec, Canada. This prior art system shares the same drawback as the CosmoPost.TM. system in that the posts are only available in preformed sizes and diameters. Again, special proprietary drills must be used in the canal preparation.
The root canal void created for using such prior art pre-formed posts are typically circular in cross-section as is shown in prior art FIG. 6A. As a result the dentist may not be able to remove all of the diseased pulp while retaining the necessary root canal void shape.
Posts are subject to high stresses once the restoration is complete and therefore the ceramic material used in the CosmoPost.TM. system and similar systems must be very strong. However, that strength prevents flexibility in fashioning the post. Other ceramic materials such as commonly available polymer/ceramic composites do not possess enough strength to be suitable material for root canal posts.
Therefore, it would be advantageous to have a tooth restoration system which combines the aesthetic qualities of an all-ceramic root canal restoration system with the strength of a conventional PFM system. It would be further advantageous for such a system to allow the convenient fabrication of a post which molds itself to the root canal and yet still possesses high structural strength.